Polyvinyl chloride (PVC) polymers have been used to produce food films for many years. There are only a few plasticizers that have the US Food and Drug Administration (xe2x80x9cFDAxe2x80x9d) approval and performance characteristics needed to plasticize PVC for food wrap applications. The plasticizer used most often to produce these wraps is dioctyl adipate (DOA). PVC compounders are always interested in reducing costs and improving performance.
Performance can be improved by reducing plasticizer volatility. That is, during the production of a PVC film, a portion of the plasticizer may be lost due to its volatility. If there is less plasticizer in the resulting film than desired, the desired physical properties cannot be obtained. Further, if additional plasticizer is used in the process to achieve the desired amount of plasticizer in the resulting film, then costs are increased. After the film is formed, avoiding migration of the plasticizer from the film into the food item can improve performance. Specifically as to reducing costs, one approach to reduce cost is to use a lower cost plasticizer or to blend a lower cost plasticizer with DOA.
To address the foregoing areas of possible improvement, the inventors propose a food wrap formed from polyvinyl chloride, at least one stabilizer, and a plasticizer in an amount of 10-60 parts per hundred parts polyvinyl chloride. The plasticizer may be present in an amount of 30-55 parts per hundred parts polyvinyl chloride. The plasticizer includes dioctyl terephthalate. Dioctyl adipate or another plasticizer may be used with dioctyl terephthalate. In this case, the plasticizer may contain 20 to 80 wt. % dioctyl terephthalate, or more specifically 20 to 60 wt. % dioctyl terephthalate. The food wrap may have a thickness of 1 to 80 mils.
According to a method of wrapping food, the food wrap is applied to a food article. According to a method of forming the food wrap, polyvinyl chloride is combined with the plasticizer to form a mixture. The mixture is heated and fused. Then, a film is formed from the fused mixture. Before the film can be sold as a food wrap, approval of the U.S. Food and Drug Administration for this use must be confirmed.
The present invention will now be described with reference to embodiments and examples which are given by way of example only, not limitation. As used herein, any given range is intended to include any and all lesser included ranges. For example, the range of 45-90 would include the ranges of 50-90, 45-95, 46-89, etc.
The present invention employs a film formed of polyvinyl chloride with a dioctyl terephthalate (DOTP) ester as a plasticizer. DOTP is the ester of terephthalic acid. DOTP can be used alone or in combination with other plasticizers, such as DOA. The plasticizer may be present in an amount of 10-60 parts per hundred parts polyvinyl chloride resin, (PPH). More particularly, the plasticizer may be present in an amount of 30-55 PPH. If a mixture of plasticizers is used, the mixture may contain 20 to 80 wt. % dioctyl terephthalate, and more particularly 20 to 60 wt. % dioctyl terephthalate. The wrapping film of the present invention has a number of uses but can be employed for hand wrapping various foods and for stretch wrapping them by an automatic wrapping machine.
Wrapping films according to one aspect of the present invention have a sufficiently low brittle temperature, thus allowing them be easily used to wrap refrigerated foods. Wrapping films according to one aspect of the present invention have a sufficiently high gas permeability, so that spoilage of wrapped perishable food can be avoided. Wrapping films according to one aspect of the present invention have a melt index lower than 20. Such a melt index improves film-forming properties and inhibits the formation of pin holes in the film. In addition, before the film can be sold as a food wrap, approval of the U.S. Food and Drug Administration for this use must be confirmed.
According to a method of forming the food wrap, the dry ingredients, such as polyvinyl chloride, are combined. Various stabilizers can be used. These stabilizers can be provided as solid or liquid components. The dry components are mixed and heated, and then the liquid components are added. After further mixing and heating to below the fusion temperature, the mixture is fused using conventional fusing equipment. The film is made from the PVC/DOTP composition at a temperature of 150 degrees to 230 degrees C. by a conventional film-forming method, for example, the T-die method, the inflation method and calendar roller method. The T-die method and the inflation method are described in U.S. Pat. Nos. 2,736,066 and 2,878,521. The wrapping film has a thickness in the range of about 5 to about 100 xcexcm, more particularly a thickness of 0.5 to 5 mils, and still more particularly a thickness of 10 to 30 microns.
Wrapping films according to one aspect the present invention have sufficient, but not excessive stickiness. To this end, the wrapping film should have an adhesive strength of not less than 20 g/2 cm2 and more particularly an adhesive strength within the range of 200 g/2 cm2 to 700 g/2 cm2. Excessive stickiness results in the following disadvantages. When the film is used to hand-wrap something, its workability is very poor because pieces of the film undesirably adhere to each other. When the film is used for automatically wrapping something, its workability is very poor and the resultant package has a bad appearance, because the film sometimes undesirably winds onto the conveyor rollers due to its high stickiness. Further, an undesirable necking phenomena often occurs when the film comes into contact with trays which receive the articles or food to be wrapped, due to the high adhesiveness of the film to the tray.
Another property related to good workability relates to smooth sliding. That is, the wrapping film should possess a smooth sliding property against rolls of a wrapping machine or against articles to be wrapped. The wrapping film should have a static friction coefficient (ASTM D1894 (1973)) of not more than 0.55.
The wrapping film should also be relatively transparent. More specifically, a transparency such that the total light transmittance is at least 80%, is desired.